508 



Experiments 



instead of air, which would be a danger signal and show the place 

 where the apparatus was faulty. 



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The animals placed under the bell-jar can be kept at a specified 

 height by means of a screen T, if it appears necessary. 



When everything is ready, the pump is started, and the reader 

 will easily understand how one can, by varying the opening of 

 the cock M, diminish more or less rapidly the pressure in the 



